Question

Which of the following factor may be regarded as the main cause of lanthanide contradiction?

• A. Poor shielding of one of the $4f$ electron by another in the subshell.
• B. Effective shielding of one of the $4f$ electrons by another in the subshell
• C. Poorer shielding of $5d$ electrons by $4f$ electrons
• D. Greater shielding of $5d$ electrons by $4f$ electrons

Answer 1

Answer: (C)

Poorer shielding of $5d$ electrons by $4f$ electrons

The lanthanide contraction is caused due to poor shielding of $5d$ electrons by $4f$ electrons.
Example: Atomic Radii of $Pd$ and $Pt$ are same when the expected radii of $Pt$ must be greater than $Pd$ as it have an extra shell.